1. Field of The Invention
This invention relates to a push-button switch that is alternately opened and closed each time an associated push-button is depressed.
2. Description of The Related Art
A conventional push-button switch comprises a depressible operating member disposed in a switch casing, a cam member secured to a lower end of the operating member for movement therewith, a return spring acting between the cam member and the bottom of the casing for urging the cam member toward its initial or inoperative position, and a switch means received within the casing for being opened and closed in accordance with the movement of the cam member. The conventional switch device further comprises a lock means for holding the cam member in its operative position upon depression of the operating member and for releasing the switch from its locked position when the operating member is depressed again.
FIG. 6 shows such a conventional locking means. Specifically, the cam member 40 has a generally heart-shaped cam groove 41. The cam groove 41 has a deep lower retaining portion 42, a right-hand side portion 43 that extends upward from the lower retaining portion 42 to a deep upper portion 45 and progressively decreases in depth towards its upper end. A step 44 is provided between right-hand side portion 43 and deep upper portion 45. The cam groove 41 also includes a left-hand side portion 48 that extends downward from the upper portion 45 to the lower retaining portion 42 and progressively decreases in depth towards its lower end. The upper portion 45 includes an upper retaining portion 46 at its central portion. The bottom surface of the cam groove 41 also includes a step 47 in the region connecting the left-hand side portion 48 and the lower retaining portion 42. Thus, the cam groove 41 forms a closed loop. An engaging member or lock pin 49 made of a metal wire has an upper end mounted on the switch casing while a lower end 49a is disposed to move along the cam groove 41. A leaf spring 50 is mounted within the switch casing and acts on the lock pin 49 to urge its lower end 49a into the cam groove 41.
In the inoperative position of the cam member 40, the lower end 49a of the lock pin 49 is retained in the lower retaining portion 42 of the cam groove 41. When the operating member is depressed, it causes the cam member 40 to move downward, so that the lower end 49a of the lock pin 49 slides along the right-hand side portion 43 of the cam groove 41 to the upper portion 45 via the step 44. Then, when the operating member is released, the cam member 40 moves slightly upward under the influence of the return spring, so that the lower end 49a of the lock pin 49 moves to the left towards the upper retaining portion 46 of the upper portion 45. This holds the cam member 40 in its operative position. When the operating member is depressed again, the cam member 40 moves downward so that the lower end 49a of the lock pin moves to the left along the upper portion 45 of the cam groove 41. When the operating member is released, the influence of the return spring causes the lower end 49a of lock pin 49 to move toward the left-hand side portion 48 of the cam groove 41 and then to move along the left-hand portion 48. In this way the lower end 49a is received in the lower retaining portion 42 via the step 47, and the cam member 40 is returned to its initial position.
Thus, when the cam member 40 is moved between its inoperative and operative positions, the lower end 49a of the lock pin 49 is moved along the cam groove 41. Since the cam groove includes the steps 44 and 47 and also has a loop-like shape, the lock pin 49 is moved back and forth in a direction perpendicular to the surface of the cam member 40. When the lock pin 49 is moved back and forth, the lock pin 49 discontinuously strikes the leaf spring 50 and produces an undesirable sound. In addition, when the lock pin 49 is abruptly moved back and forth, there is a risk that the lower end 49a of the lock pin 49 may be disengaged from the cam groove 41.